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Rocket Boosters Sail Back


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Hello everybody!


I've spent some time comparing rocket propellants suitable for pressure-feed at a launcher, and have gone away from oxygen-methane and cyclopropane to room-storable fuels (and liquid oxygen). Though they may offer a lower specific impulse, the tanks they need are lighter, resulting in slightly better stages - and safer if the fuel leaks and ignites less easily than a gas does. Amines outperform hydrocarbons as well.


The heaviest tank stores helium, and cold liquid methane needs more helium than a room-temperature fuel does. Also, a reasonable layer of microballoons-filled polymer can insulate the fuel tank from the colder helium tank and keep a simple and sturdy construction for the booster, of thick Maraging steel sheet all welded together. More detailed rationale and figures there:

Link removed


As an illustration, here's a launcher whose side boosters burn pressure-fed Pmdeta (pentamethyl-diethylene-triamine), and whose central core burns hydrogen-oxygen in Vinci engines ignited after separation. The boosters - whose number fits the payload and mission - are "cross-fed", where all engines consume propellants from the tanks of one boosters pair at a time which is separated early as it goes empty to save inert mass.




I'll describe later how the boosters shall sail back for reuse; this fits pressure-feed nicely. Or see

Link removed

if you don't want to wait.


Marc Schaefer, aka Enthalpy

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  • 1 year later...

As of mid-2013, Ariane 6 is to have two solid stages and a Vinci hydrogen stage to put 6.5 t in Geosynchronous Transfer Orbit. One or two pressure-fed liquid stages before the Vinci make my design lighter, adaptable by a factor of three, and hopefully cheap as the sailback boosters are reused:

(click to magnify)

Instead of crossfeed, the boosters throttle from 36bar to 20bar to lighten the helium tank and weigh dry just 114kg per ton of propellants (45.1 t propellants each). Expansion to 0.35bar brings at sea level isp=2408m/s=246s and 1335kN each, and in vacuum isp=3043m/s=310s. The fairing is estimated at 2.6t.

2,3 or 4 boosters ignite at lift-off; if using 6 boosters, two ignite after the first four are separated. At the cone that tops the central stage, each side booster shares one thrust point with the adjacent side booster, and an internal truss connects the thrust points.

Fastening the boosters high reduces the bending moment on the central stage, whose skin is of extruded AA6082 panels as I describe there:
B=20mm b=18mm a=45° resist 715kN/m without margin, or sufficient 7.6MN*m with D=3m.

The central stage contains up to 28.2t of propellants depending on the lower stage(s). It weighs 2.1t empty with all equipment and adapters. The vinci brings isp=4560m/s=465s and 180kN once the side boosters are separated. The roll and insertion Verniers can burn hydrogen fed by electric pumps, or Pmdeta which enables pressure-feed.

An optional added stage with the Solar rocket engine I describe there
can start with 12.5t from low-Earth-orbit to put 7.3t in geosynchronous orbit.

More explanations will come some day about how the boosters splash down and sail back to the launch pad.

Marc Schaefer, aka Enthalpy

Edited by Enthalpy
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  • 11 months later...

This shall launch the manned Mars mission I describe there

with performance flexibility, and cheaply as it expends only two RS-68 and reuses its sailback boosters. It's as bulky as a Shuttle but with more side boosters and a fairing on top. Click for full size.




The second stage weighs 43.7t empty plus 709t or propellants, its 3.4m wide RS-68 bring 4204m/s=429s and 3.53MN. Each booster weighs 50.7t empty and expands 419.4t of oxygen and Pmdeta from 36bar (ending at 19bar for 2.8g) to 0.56bar in D=4.4m for 2922m/s=298s @vac and 9.3MN, 2509m/s=256s @sl.




8 positions permit 4, 6 or 8 booster, while 9 permit 3, 6 or 9. I've only evaluated simultaneous boosters; six wouldn't push well two inert ones at the end, but throttling two early to keep them longer, possibly while the second stage pushes, looks interesting.


Most second stage's walls consist of aluminium extrusion as I describe there


5690kg D=11m fairing, AA6005A, 45° 1mm 1mm. Thinner would improve.
2397kg D=11m adapter, AA6005A, 60° 1mm 1mm B=38mm. The Leo payload rests on top.
1749kg D=8 to 11m cone, AA6082, 60° 1.5mm 1.5mm B=53mm.
380kg top oxygen elliptic head, AA7022, 1.7mm.
2120kg upper 3.6m of oxygen tank, AA7022, 45° 2.8mm 2mm.
1855kg lower 2.7m of oxygen tank, AA7022, 45° 3.5mm 2mm.
1258kg bottom oxygen spherical head, AA7022, 4.5mm.
169kg foam

4800kg intertank truss. 16 nodes (if 4 6 8 boosters) and 2+2 levels. Heat-treated Ti-Al6V4 tubes, upwards OD=141.4mm ID=130mm. Downwards lighter, stiffeners inwards also. Is it oversized?

380kg top hydrogen elliptic head, AA7022, 1.7mm.
11980kg 25.1m hydrogen tank, AA7022, 45° 2.0mm 2mm.
544kg bottom hydrogen elliptic head, AA7022, 2.4mm.
395kg foam

400kg engines truss
13800kg two wider RS-68
300kg command and control
1000kg undetailed

The structural tanks weigh 39kg/t of propellants, the empty stage 29.7t or 61kg/t. I didn't compare with a common head and boosters pushing a truss between the oxygen tank and the payload.

The sailback boosters are of welded maraging as usual, they weigh 121kg/t of propellants thanks to throttling.


Inert masses are heavy here. Three stages instead, the third's RS-68 with a 6m extensible nozzle, the second's three RS-68 3.4m wide, would weigh only 2760t to put 160t into Leo - but cost probably more. A corresponding drawing may follow.

Marc Schaefer, aka Enthalpy

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  • 6 months later...

Here are, very late meanwhile, at least drawings to explain that the paraglider that splashes the booster on the Ocean also sails it back home, usd as a propelling kite.






Kites serve already to propel cargo boats and are highly automated:


in gently trade winds, they would cover 500km in 2 days. Perfect at Tanegashima, Kourou... maybe at Cape Canaveral, Goheung and Sriharikota depending on the traffic. Bad idea at Baikonur.


Pressure-fed liquids combine well with reused boosters navigating the Ocean: they are already as strong as a boat hull, they float and keep clean... This makes them better candidates than solids, and they are more efficient as well.


Sailing back takes no additional fuel, is technically simpler than flying, needs no wings, engine, landing gear, and the certification and integration to traffic is easier for a boat.

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  • 1 year later...

News report that Launcher One is to grow to put ~300kg on sun-synchronous orbit, and also that the French Onera targets the same kind of payloads - not only because Americans do it , but because new satellite operators want to put huge constellations in orbit.

And, mamma mia, Onera too wants to start from an aeroplane despite Europe has the perfect spaceport in Guyana towards East and North. Worse: they want to use hydrogen peroxide. Porca miseria, do they have anything agaist nitroglycerine? And then, of course, turbopumps.

Well, my pressure-fed equivalent of Tronador can, without modification, also put 290kg on a 800km sun-synchronous orbit. Suggested there
http://forum.nasaspaceflight.com/index.php?topic=26645.0as reply #23 on 07/18/2012
but it's very close to my pressure-fed equivalent of Launcher One suggested there
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2554&start=50#p38614on Jul 16, 2012
and anyway, here's the drawing again:



Two stages, starts from the ground, made of cheap materials, burns safe propellants, and decently efficient. I don't really find an excuse to have pumps at that launcher size, but at least, Rocket Lab
does it in two stages from the ground with batteries and electric pumps as I suggested there
not very costly, and it does improve the performance.

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  • 2 months later...

Reused "sailback" boosters can replace the solids at the new definitive version of Ariane 6.



Here they have the same 143.7t and D = 3.5m as the solids. The D=2.4m nozzle pushes 3500kN in vacuum (2500kN at the end) and 3040kN sea level. 197:100 Pmdeta:O2 expands from 36bar (26bar at the end) to 62kPa, achieving Isp = 2897m/s = 295s in vacuum and 2518m/s = 257s at sea level. The solids achieve 2741m/s = 280s in vacuum.

The thick welded Maraging steel (not cold-worked) lets the empty boosters weigh 126kg per ton of propellants while the solids' wound graphite achieves 84kg per ton. This cancels out the propellant efficiency.

The sailback boosters are compatible, slightly taller, safer to manufacture and use, and reused.

Marc Schaefer, aka Enthalpy

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  • 2 months later...

Here are optimizations for a pressure-fed stage with wound graphite tanks.

These apply to a "sailback" first stage with a graphite sandwich (it works for raceboats) cylinder holding the tanks. Helium from a high-pressure tank at oxygen temperature (heat pipe?) tops each propellant at its temperature all the time. The chamber and propellant pressures drop *0.45 at the end as does the thrust. The nozzle expands to 0.6bar at the beginning. The stage provides 4000m/s vacuum equivalent.

Composite plies work at 1200MPa at all tanks, the cylinder weighs 10kg per ton of propellants, the engine 20kg/t, the paraglider and undetailed items hers 15kg/t. The injectors are 88% efficient, vanes 95% when not throttling additionally.

The best chamber pressure is 49bar at beginning with Pmdeta, but 45bar is as good and saves helium and graphite. Logically more than 36bar, the optimum with heavier steel.

Pmdeta remains an excellent choice with graphite: hard to light, nearly nontoxic, mass-available and cheap, good Isp, and its nitrogen saves cold oxygen hence helium and tank mass.

  • Bulky and cold methane is the worst performing with graphite too.
  • Flammable spiropentane, azetidine and cyclopropane would but outperform Pmdeta: 3.4%, 2.1% and 2.1% more payload per stage. This makes 10% more mass in Gto, not worth the risk.
  • Boctane (cyclobutylcyclobutane) is as good as Pmdeta, Rg-1 and Jp-10 are worse than Pmdeta and no better than the cheap cis-pinane.
  • Strained amines like diazetidylcyclopropane are as efficient as cyclopropane, hard to light, and easier to produce than strained hydrocarbons. They save helium and graphite too. Best improvement to Pmdeta.
  • Trimethyltriazinane and the viscous Deta are 1% less efficient than Pmdeta, and they save helium and graphite. A eutectic with Pmdeta would be nice.

A first stage with 150t propellants would carry 1.8t helium (36k€ in 2015), still there at the end of propulsion and possibly when the stage lands at the coast.

A graphite pressure-fed first stage delivers 4000m/s easily. 5000m/s are reasonable, 6000m/s overstretched and an Ssto impossible. This tops steel tanks by 1000m/s to save one stage or enable other stage combinations.

The construction is already described for light tanks and pumped propellants:
The tanks are just thicker here. Here's an example of arrangement - some tanks could be oblate or toroids at a short stage:



The nozzle of a second stage can expand to a lower pressure, for instance to push 180kN in D=2.2m with Pmdeta, and then 25bar in the chamber is optimum as it lightens the tanks, but 20bar is nearly as good. With the smaller engine weighing 10kg per ton of propellants, the cylinder 10kg/t, undetailed 10kg/t without paraglider, and helium filled to 165bar, the stage without electronics weighs 54kg/t, wow. Expansion to 2.2kPa achieves Isp=3537m/s=361s, wow again. 5500m/s is easy for such a stage, 7000m/s reasonable and 8000m/s overstretched.

Marc Schaefer, aka Enthalpy

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  • 2 weeks later...

My estimates as above suggest a P80 wounded graphite vessel lighter than it is, so I've tweaked the figures. Presently, I get pressure tanks of wounded graphite 0.53* as heavy as Maraging steel.

Reoptimization give initial 40bar and 20bar in the chamber of a first and escape stages.


Liquid oxygen and lighter tanks let a pressure-fed first stage bring deltaV=4500m/s naturally, which neither solids nor steel tanks do well. Then, a stage with a single Vinci brings a Soyuz-class payload to Gto or Leo. The simpler make-up and the reused first stage shall make cheaper launches.


An alternative pressure-fed second stage brings lighter payloads to Leo from Gnd+4000m/s for less money than the Vinci. Gto in two pressure-fed stages stays unreasonable.

An optional pressure-fed third stage goes to Mars transfer, geosynchronous orbit, lunar orbit from Leo-200m/s or Leo. Foam and multilayer insulation on the oxygen ballon held by polymer belts let evaporate few kg per day, needing no active cooling.

An alternative optional third stage pumps hydrogen and oxygen with 100kW electricity from a 50kg fuel cell. Again, multilayer insulation spares active cooling even to land on the Moon in one stage from Leo+700m/s - the payload mass still needs legs. The stage starts from Leo-500m/s for Gto, especially on top of a pressure-fed second stage.

Every launcher should have a liquid oxygen escape stage available, flexible and hugely better than present solids and storables.

Stages data:

Propell Dry Thrust Thrott Nozzles Chamb Isp
kg kg kN d (m) bar s
4103 500 15 4* 1.00 60 492 3rd hydrogen
3704 500 8 0.50 4* 1.00 20 398 3rd Pmdeta
<23430 2174 171 yes 1* 1.25 443 2nd Vinci
31429 2271 390 0.30 1* 1.60 30 330 2nd Pmdeta
160600 14090 3272 0.39 2* 1.65 40 302 1st Pmdeta @vac
160600 14090 2840 2* 1.65 40 262 1st Pmdeta @1at

My sunheat engine would bring performance to Gso and the planets here too

In the D=5m fairing, Atlas and Delta accommodate D=4572mm payloads, as much as Ariane V does.

Marc Schaefer, aka Enthalpy

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  • 4 years later...

For suborbital rockets too, be it science or tourism, pressure-fed liquids are an interesting option. >100km altitude needs efficient engines, and optimizing solids takes much development, while liquids provide naturally a good ejection speed. Roll control is easier too. In many cases, one liquid stage can replace two solids.

The same propellants selection applies: oxygen, helium, and a storable fuel, better an amine like Pmdeta. And here too, graphite fibre tanks outperform steel tanks. Electric pumps and batteries would outperform pressurized tanks.

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